This project represents the continuation of an effort to characterize and quantify the development of auditory processing skills in preschool and school-aged children. There are two distinguishing features of this effort. First, each child is tested repeatedly in all conditions of an experiment producing precise estimates of both between and within subjects variability. Second, the psychophysical procedures are adaptations of the rigorous forced-choice paradigms routinely used to assess adult auditory function. This permits meaningful comparisons of adult and child performance. Published results from the previous funding period show that the average frequency resolution, temporal resolution, and spectral pattern discrimination skills of children do not reach adult levels until age six or later. However, variability in performance among children is much higher than among adults; some children demonstrate adult-like performance as early as age three. Recent results suggest that this variability may result from the fact that the performance of some children is especially susceptible to the interference caused by uncertainty and the presence of distractor stimuli. Thus, it does not appear necessary to assume that children have an underdeveloped auditory system; some may simply use suboptimal listening strategies. A major goal of the current experiments is to understand and characterize in detail the listening strategies used by children in a variety of auditory tasks. Of special interest is how children separate relevant from irrelevant information, or auditory "foreground" from auditory "background". One set of experiments will use a simplified version of the powerful sample-discrimination paradigm in which various aspects of a child's performance in discriminating tone patterns are compared to the performance of the optimal listener specified by information and detection theory. This paradigm produces detailed information on how the various components in a pattern are weighted and combined. A second set of experiments will measure how children use spatial information to separate 'foreground" from "background", for example to separate relevant speech from irrelevant competition in a reverberant listening environment such as a classroom. These experiments will use discrimination tasks to determine the distracting effects of single echoes, and simple localization tasks to assess the ability of children to use the complex spectral cues (provided by the pinnae) that must be learned. All of the experiments will initially involve children from three to eight years of age who are developing typically, and whose hearing is judged to be normal on the basis of standard audiometric assessment.